Electric fuse having blown fuse indicator

ABSTRACT

The spring-biased indicator pin of a blown fuse indicator is normally restrained by a fusible element arranged with the preponderant portion of its length in a plane at right angles to the axis of said pin, projecting through a bore in said pin and subjected to a shear-action by the spring-bias of said pin.

United States Patent 1191 1111 3,824,520 Knapp, Jr. 14 1 July 16, 1974[541 ELECTRIC FUSE HAVING BLOWN FUSE 3,697,916 10/1972 Belcher et al337/161 INDICATOR 3,713,064 1/1973 Jacobs, Jr. 337/161 [75] inventor:Edward J. Knapp, Jr.,

Newburyport, Mass.

[73] Assignee: The Chase-Shawmut Company,

Newburyport, Mass. [22] Filed: Dec. 12, 1973 21 App]. No.1 424,042

[52] U.S. Cl 337/161, 337/265, 337/295 [51] Int. Cl. H01h 85/12 [58]Field of Search 337/146, 161, 256, 265, 337/276, 293, 295

[56] References Cited UNITED STATES PATENTS Salzer 337/161 PrimaryExaminer-G. Harris Attorney, Agent, or FirmErwin Salzer [57] ABSTRACTThe spring-biased indicator pin of a blown fuse indicator is normallyrestrained by a fusible element arranged with the preponderant portionof its length in a plane at right angles to the axis of said pin,projecting through a bore in said pin and subjected to a shearaction bythe spring-bias of said pin.

5 (ilaims, 6 Drawing Figures BACKGROUND OF THE INVENTION This inventionrelates to blown fuse indicators for electric fuses, and its principalaims are to simplify the construction and assembly of blown fuseindicators.

A more specific object of this invention is to improve blown fuseindicators for polyphase fuses having stab contacts, i.e., fuses whereinseveral fuse units, each for controlling excess currents in one phase ofa polyphase circuit, are integrated to form a structural unit that canbe inserted by means of stab contacts into a polyphase circuit to beprotected against excess currents. Such polyphase fuses are well knownin the art and one embodiment thereof is disclosed in U.S. Pat. No.

3,319,027 to P. C. Hitchcock, issued May 9, 1967 for ENCAPSULATED FUSESTRUCTURE FOR POLY- PHASE CIRCUITS. This patent shows a type of blownfuse indicator which, and variations of which, have been widely adoptedin connection with polyphase fuses as, for instance, the polyphase fusesnot featuring stab contacts disclosed in U.S. Pat. No. 3,671,910 to F.J. Kozacka, issued June 20, 1972 for COMPACT POL- YPHASE FUSE. Referencemay be had to the two aforementioned patents as representative of thestate of the art in regard to blown fuse indicators, and morespecifically to blown fuse indicators for polyphase fuses.

Polyphase fuses include often spaced metal strips conductivelyinterconnected by current-carrying fusible elements having a relativelylow resistance and fusible restraining elements for the blown fuseindicator having a relatively high resistance and connected in parallelto the former. The fusible restraining elements for the blown fuseindicator are generally oriented and arranged in a way entirelydifferent from the way the current carrying fusible elements areoriented and arranged. This results in difficulties which are eliminatedby the present invention.

SUMMARY OF THE INVENTION Fuses embodying this invention include anindicator pin of electric insulating material having an indicating frontend, a rear end defining a transverse passageway and a spring-supportingcollar or flange of increased diameter arranged between said front endand said rear end of said pin. A plate of electric insulating materialis arranged at right angles to the axis of said pin and has an aperturearranged in registry with said pin. The rear end of said pin projectsinto said aperture to such an extent that said pin extends beyond theplane of said plate remote from said front end of said pin. Fusesembodying this invention further include fusible currentcarrying elementmeans having a relatively low resistance and fusible restraining elementmeans having a relatively high resistance connected in parallel to saidfusible current-carrying element means. The preponderant portionof thelength of said fusible restraining element means is arranged in saidplane of said plate remote from said front end of said pin and saidfusible restraining element means is threaded through said transversepassageway in said rear end of said pin. A helical spring surrounds saidrear end of said pin, rests with one end thereof against saidspring-supporting collar or flange of said pin and subjects the portionof said fusible restraining element means threaded through saidpassageway in said rear end to said pin to a shearaction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of apolyphase fuse having stab contacts for insertion of the fuse into anelectric polyphase circuit, one portion of the housing and of the coverof the fuse being broken away to expose to view I the internal structureof the fuse;

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIGS. 1-3 of thedrawings, numeral 1 has been applied to indicate a prismatic housing forthree fuse units, each for one phase of a polyphase three phase circuit.Each of the three fuse units can be inserted by means of stab contacts 2into contacts of a polyphase or three phase fuse holder (not shown).Housing 1 defines three substantially prismatic chambers closed atthe'sides and the bottom thereof and having an open end. FIG. 1 showsone of these three chambers and reference numeral 3 has been applied toit. Chamber-3 is also shown in FIG. 2. Reference numeral 4 has beenapplied to indicate the open side of chamber 3 which is normally closedby a cover 5. Housing 1 and cover 5 are of an electric insulatingmaterial, preferably a molded synthetic resin. Chamber 3 houses a pairof metal strips 6 arranged adjacent and parallel to two sides or sidewalls thereof. Metal strips 6 are conductively interconnected by fusiblecurrent-carrying element means preferably formed by perforated ribbons 7of silver. Metal strips 6 have external ends projecting transverselythrough the bottom 25 of chamber 3 to the outside thereof. The endsofstrips or plates 6 outside housing 1 and outside chamber 3 form theaforementionedstab contacts 2. Cover 5 may be affixed to housing 1 byany desired fastener means, e.g., screws (not shown) projecting throughthe four corners of cover 5 into housing 1. Cover 5 has a recess 8housing an indicator pin 9 of electric insulating material. Indicatorpin 9 has a front end and a rear end and the latter defines a transversepassageway 10. Indicator pin 9 has a spring flange or collar 11 ofincreased diameter arranged between the front end and the rear end ofpin 9. The plate 12 of electric insulating material is arranged at rightangles to the axis of pin 9 and has an aperture 13 arranged in registrywith pin 9. The rear end of pin 9 projects into aperture 13 to such anextent that the rear end-of pin 12 extends beyond the plane of plate 12remote from the front end of pin 9. In addition to the fusiblecurrent-carrying element means 7 having a relatively low resistance eachfuse unit is provided with a fusible restraining element 14 having arelatively high resistance. Elements 7 and 14 are connected inparallel,i.e., both elements conductively interconnect .the pair of metal platesor strips 6 of one fuse unit. The preponderant portion of the length offusible restraining element 14 is arranged in the plane of plate 12remote from the front end of pin 9. As shown in FIG. 3, element 14 isformed by a high resistance wire which is threaded through transversepassageway 10 in pin 9. The rear end of pin 9 is surrounded by a helicalspring 15 which rests with the upper end thereof against flange orcollar 11 of pin 9. The other end of spring 15 rests against plate 12and thus subjects to a shear action the portion of fusible restrainingelement 14 threaded through passageway 10 in pin 9. Plate 12 is arrangedin a plane parallel to that of cover and has shoulder-formingprojections l6 engaging projection-receiving slots 17 in the ends ofmetal strips or plates 6 adjacent cover 5. By virtue of its shouldersplate 12 has edges clamping bent ends of fusible restraining element 14against the ends of metal strips 6 adjacent cover 5.

A gasket 18 at the bottom of chamber 3 precludes the outflow'ofpulverulent arc-quenching filler 19 from the inside of housing 1 andchamber or chambers 3 through the apertures in bottom 25 providedtherein for the passage of the stab-contact-forming ends of metal stripsor plates 6.

Fusible elements 7 carry the load current as long as it is notexcessive. During this period of time wire 14 virtually does not carryany current since its resistance exceeds by far that of current-carryingfusible elements 7 by which it is shunted. When the latter melt andbreaks take their place, wire 14 begins to carry current and is heatedby i 'r losses occurring therein. Heat dissipation from wire 14 isminimized at thepoint thereof where wire 14 projects through passagewayin pin 9. Therefore the temperature along wire 14 forms a steep peak atthe region or point thereof where it is subjected by spring to a shearaction. As a result of this distribution of temperature and theaforementioned shear action the current path formed by wire 14 israpidly broken when it is caused to carry current and pin 9 propelledaxially outwardly under the action of spring 15, thus indicating thatthe fuse has blown.

In FIGS. 4, 5 and 6 the same reference characters as in FIGS. 1-3 with aprime added have been applied to indicate like parts. Therefore thestructure shown in FIGS. 4, 5 and 6 calls for a detailed descriptiononly inasmuch as it differs from that of FIGS. 1-3 which has beendescribed above in detail.

Speaking generally, in the structure of FIGS. 4-6 cover 5 performs thefunction of parts 5 and 12 of the structure of FIGS. 1-3. To be morespecific, cover 5" performs the function of closing the open end ofchamber 3 and of supporting a fusible restraining element 14 arranged onthe inner surface of cover 5'.

In the structure of FIGS. 4-6 recess 8' in cover 5 houses a cap 20' ofelectric insulating material and helical indicator-pin-biasing spring 15rests with one end thereof against cap 20 and with the other end thereofagainst flange or spring collar 11' of pin 9'. The high resistancefusible pin-restraining element 14 is formed by a narrow strip of sheetmetal threaded through transverse passageway 10' in the rear end of pin9' which, in turn, projects through the end surface of cap 20. Element14' has ashort length of reduced crosssectional area coextensive withpassageway 10'. As a result, a steep temperature peak occurs at theportion of element 14' inside of passageway 10'. The ends of fusiblerestraining element 14' are affixed, e.g., by means of screws 21, to theinner surface of cover 5. The ends of element 14 are in physical contactwith and hence conductively connected to a pair of contact leaf springs22'. Cover 5, cap 20', pin 9, spring 15, fusible element 14 and contactleaf spring 22 form a self-contained structural unit that can be removedas a unit from housing 1 and affixed as a unit to housing 1'. When theaforementioned cover unit 5 20, 9', l5',l4, 22 is caused to engagehousing 1" (as shown in FIGS. 4-6) contact leaf springs 22' come to reston the edges of strips or plates 6' adjacent to cover 5. As a result,fusible element 14' is conductively connected across strips or plates 6'in parallel to fusible elements 7. I

Fusible element 14' becomes current-carrying after fusion of fusibleelements 7'. This allows spring 15 to form a break at the point offusible element 14' where it is threaded through the rear end ofindicator pin 9'. This, in turn, frees indicator pin 9 and thus allowshelical spring 15 to propel pin 9' outwardly to the indicating positionthereof.

Contact leaf springs 22 are effective means for conductively connectingthe ends of fusible restraining element 14' to metal strips 6. It is,however, apparent that other contact means might be substituted forcontact lead springs '22.

I claim as my invention! 1. In an electric fuse having a blown fuseindicator the combination of a. an indicator pin of an electricinsulating material including an indicating front end, a rear enddefining 'a transverse passageway and a springsupporting collar ofincreased diameter arranged between said front end and said rear end ofsaid b. a plate of electric insulating material arranged at right anglesto the axis of said pin and having an aperture arranged in registry withsaid pin, said rear end of said pin projecting into said aperture tosuch an extent that said rear end of said pin extends beyond the planeof said plate remote from said front end of said pin;

0. fusible current-carrying element means having a relatively lowresistance and fusible restraining element means having a relativelyhigh resistance connected in parallel to said fusible current-carryingelement means, the preponderant portion of the lengthtof said fusiblerestraining element means being arranged in said plane of said plateremote from said front end of said pin and said fusible restrainingelement means being threaded through said transverse passageway in saidrear end of said pin; and

(I. a helical spring surrounding said rear end of said pin, resting withone end thereof against said spring-supporting collar of said pin andsubjecting to shear action the portion of said fusible restrainingelement means threaded through said passageway in said rearend of saidpin.

2. In an electric fuse as specified in claim 1 the combination' of a. ahousing defining a substantially prismatic chamber closed at the sidesand at the bottom thereof and having an open end;

b. a pulverulent arc-quenching filler inside said chamber submersingsaid fusible current-carrying element means;

c. a pair of spaced metal strips inside said chamber arranged adjacentand parallel to two sides thereof and conductively interconnected bysaid fusible current-carrying element means, said pair of metal stripshaving external ends projecting transversely through said bottom of saidchamber to the outside thereof and forming a pair of stab contacts;

(1. a cover affixed to said housing and closing said open end of saidchamber, said cover having a recess housing said indicator pin;

. said plate of electric insulating material being arranged in a planeparallel to the plane of said cover and said fusible restraining elementbeing arranged on the side thereof remote from said cover, said platehaving shoulder-forming projections engaging projection-receiving slotsin the ends of said pair of metal strips adjacent said cover and havingedges clamping the ends of said fusible restraining element against saidends of said metal strips adjacent said cover.

3. An electric fuse as specified in claim 1 wherein a. said fusiblecurrent-carrying element means are arranged in a housing defining asubstantially prismatic chamber closed at the sides and at the bottomthereof and having an open end;

b. a pulverulent arc-quenching filler is arranged inside said chambersubmersing said fusible currentcarrying element means;

c. a pair of spaced metal strips inside said chamber is arrangedadjacent to two sides thereof, said pair of metal strips beingconductively interconnected by said fusible current-carrying elementmeans and said pair of metal strips having external ends projectingtransversely through said bottom of said chamber to the outside thereofand forming a pair of stab contacts;

d. said plate of electric insulating material being affixed to saidhousing in such a way as to form a cover for said open end of saidchamber, said plate having a recess housing said indicator pin andsupporting said fusible restraining element means on the side thereofadjacent said chamber; and

e. a pair of contacts supported by said plate of electric insulatingmaterial on said side thereof adjacent said chamber, said pair ofcontacts being conductively interconnected by said fusible restrainingelement means and each of said pair of contacts engaging one of saidpair of metal strips at the ends thereof adjacent said plate of electricinsulating 6 material.

4. An electric low-voltage fuse including a. a housing of syntheticresin defining a substantially prismatic chamber closed at the sides andat the bottom thereof and having an open end;

b. a pulverulent arc-quenching filler inside said chamber;

c. a pair of spaced metal strips inside said chamber arranged adjacentand parallel to two said sides thereof, said pair of metal strips havingends projecting transversely through said housing to the outside thereofand forming a pair ofterminals for connecting said fuse into an electriccircuit;

d. fusible element means inside said chamber immersed in said filler andconductively interconnecting said pair of metal strips;

e. a' cover affixed to said housing and closing said open end of saidchamber;

f. a blown fuse indicator on and supported by said cover, said blownfuse indicator including a springbiased indicator pin; and r g. meansnormally restraining said indicator pin against the spring bias thereof,said restraining means including a fusible pin-restraining elementprojecting transversely through said pin and being arranged with thepreponderant portion of the length thereof substantially parallel tosaid cover, said fusible pin-restraining element having ends juxtaposedto the ends of said pair of metal strips adjacent said cover and beingclamped under pressure against said ends of said pair of metal stripsadjacent said cover.

5. An electric fuse as specified in claim 4 including a plate ofelectric insulating material arranged parallel to said cover, said platehaving an aperture arranged in registry with said indicator pin, saidindicator pin having a projection extending into said aperture and saidprojection having a transverse bore, said fusible pinrestraining elementbeing arranged on the side of said plate remote from said cover andextending from one of said pair of metal strips through said bore insaid projection of said indicator pin to the other of said pair of metalstrips.

1. In an electric fuse having a blown fuse indicator the combination ofa. an indicator pin of an electric insulating material including anindicating front end, a rear end defining a transverse passageway and aspring-supporting collar of increased diameter arranged between saidfront end and said rear end of said pin; b. a plate of electricinsulating material arranged at right angles to the axis of said pin andhaving an aperture arranged in registry with said pin, said rear end ofsaid pin projecting into said aperture to such an extent that said rearend of said pin extends beyond the plane of said plate remote from saidfront end of said pin; c. fusible current-carrying element means havinga relatively low resistance and fusible restraining element means havinga relatively high resistance connected in parallel to said fusiblecurrent-carrying element means, the preponderant portion of the lengthof said fusible restraining element means being arranged in said planeof said plate remote from said front end of said pin and said fusiblerestraining element means being threaded through said transversepassageway in said rear end of said pin; and d. a helical springsurrounding said rear end of said pin, resting with one end thereofagainst said spring-supporting collar of said pin and subjecting toshear action the portion of said fusible restraining element meansthreaded through said passageway in said rear end of said pin.
 2. In anelectric fuse as specified in claim 1 the combination of a. a housingdefining a substantially prismatic chamber closed at the sides and atthe bottom thereof and having an open end; b. a pulverulentarc-quenching filler inside said chamber submersing said fusiblecurrent-carrying element means; c. a pair of spaced metal strips insidesaid chamber arranged adjacent and parallel to two sides thereof andconductively interconnected by said fusible current-carrying elementmeans, said pair of metal strips having external ends projectingtransversely through said bottom of said chamber to the outside thereofand forming a pair of stab contacts; d. a cover affixed to said housingand closing said open end of said chamber, said cover having a recesshousing said indicator pin; e. said plate of electric insulatingmaterial being arranged in a plane parallel to the plane of said coverand said fusible restraining element being arranged on the side thereofremote from said cover, said plate having shoulder-forming projectionsengaging projection-receiving slots in the ends of said pair of metalstrips adjacent said cover and having edges clamping the ends of saidfusible restraining element against said ends of said metal stripsadjacent said cover.
 3. An electric fuse as specified in claim 1 whereina. said fusible current-carrying element means are arranged in a housingdefining a substantially prismatic chamber closed at the sides and atthe bottom thereof and having an open end; b. a pulverulentarc-quenching filler is arranged inside said chamber submersing saidfusible current-carrying element means; c. a pair of spaced metal stripsinside said chamber is arranged adjacent to two sides thereof, said pairof metal strips being conductively interconnected by said fusiblecurrent-carrying element means and said pair of metal strips havingexternal ends projecting transversely through said bottom of saidchamber to the outside thereof and forming a pair of stab contacts; d.said plate of electric insulating material being Affixed to said housingin such a way as to form a cover for said open end of said chamber, saidplate having a recess housing said indicator pin and supporting saidfusible restraining element means on the side thereof adjacent saidchamber; and e. a pair of contacts supported by said plate of electricinsulating material on said side thereof adjacent said chamber, saidpair of contacts being conductively interconnected by said fusiblerestraining element means and each of said pair of contacts engaging oneof said pair of metal strips at the ends thereof adjacent said plate ofelectric insulating material.
 4. An electric low-voltage fuse includinga. a housing of synthetic resin defining a substantially prismaticchamber closed at the sides and at the bottom thereof and having an openend; b. a pulverulent arc-quenching filler inside said chamber; c. apair of spaced metal strips inside said chamber arranged adjacent andparallel to two said sides thereof, said pair of metal strips havingends projecting transversely through said housing to the outside thereofand forming a pair of terminals for connecting said fuse into anelectric circuit; d. fusible element means inside said chamber immersedin said filler and conductively interconnecting said pair of metalstrips; e. a cover affixed to said housing and closing said open end ofsaid chamber; f. a blown fuse indicator on and supported by said cover,said blown fuse indicator including a spring-biased indicator pin; andg. means normally restraining said indicator pin against the spring biasthereof, said restraining means including a fusible pin-restrainingelement projecting transversely through said pin and being arranged withthe preponderant portion of the length thereof substantially parallel tosaid cover, said fusible pin-restraining element having ends juxtaposedto the ends of said pair of metal strips adjacent said cover and beingclamped under pressure against said ends of said pair of metal stripsadjacent said cover.
 5. An electric fuse as specified in claim 4including a plate of electric insulating material arranged parallel tosaid cover, said plate having an aperture arranged in registry with saidindicator pin, said indicator pin having a projection extending intosaid aperture and said projection having a transverse bore, said fusiblepin-restraining element being arranged on the side of said plate remotefrom said cover and extending from one of said pair of metal stripsthrough said bore in said projection of said indicator pin to the otherof said pair of metal strips.